Tire air pressure

[Jim Lee]

Hi,
I am just curious as to what kind of pressure folks are running around with. I have a TR3A and have all four set to 30 lbs. The main thing I am wondering is if I could safely lower the pressure and get a slightly better ride. I know it
is never going to be a Town Car, and I would not want it to be
but the roads in my area have been getting real beatup with over weight construction trucks and it is getting kind of irritating. I have Spax gas shocks in the front and the original lever shocks in the back. I know that I can adjust the shocks but it seems like I feel most of the hard hits in the rear. The kind of driving I do is just cruising around without squealing tires or testing the limits of my suspension. Most of the time.

Thanks very much,
Jim Lee

 

[Andrew Mace]

Jim, you might try dropping down to around 27-28, but I wouldn't want to go much lower.

As for the "hard hits in the rear," you might try painting the edges of the springs lightly with engine oil (as recommended in the service manual). It could be that the spring leaves simply aren't sliding as freely against each other as they should, which would lead to a harder ride.

 

[myspitfire]

Hi Jim;My Spit is using 175/70/r13 and i'm using what the manual states for the factory stock(155/80/r13 which is 24 rear & 26 in front give or take a # or 2.I find this pressure utilizes the side wall tread for better cornering ability.BUT for storing the car as it is now i fill them to max allowable 35#,which some say is a better storage pressure.The lesser pressure puts more rubber on the road.Higher summer road pressures shocks the car to much plus the higher the temperature goes the more pressure builds up in the tire.,then visa-versa when they cool down.
KensWhitelightning

 

[swift6]

Less pressure might mean 'more rubber on the road' but it also means softer/more flexible sidewalls that decrease handling, fuel mileage, acceleration and braking. Modern radials work better with higher pressures than most Triumph manuals ask for. If you are using modern radials than 27-30psi are better numbers. The number on the sidewall of the tire is based on the max load rating of the tire, NOT your car.

 

[foxtrapper]

My tire pressure varies tremendously from vehicle to vehicle, and application to application.

The Spitfire currently runs 26/22 psi front and rear.

The Volvo runs 44 psi front and rear.

The truck runs around 30-35 psi typically on the road.

+1 on Andrews comment about lubricating the leaf springs. It makes a heck of a difference!

 

[Geo Hahn]

I like a higher pressure on the TRs -- something around 34 front & 36 rear. Yes, it makes the ride a bit harsher but nothing uncomfortable if the rear shocks are doing their job.

Higher pressure in the front may exaggerate the already present tendency to oversteer, which some drivers find enjoyable and navigators invariably find alarming.

Higher pressure in the front may also make low-speed turning less of an effort ona TR3.

 

[MadMarx]

Depending on the tires.

With semi-slicks 24-26 pounds are okay.

Normal street tires need more than 30 pounds.

 

[NickMorgan]

Jim,
I remember this being discussed by the TR Register some years ago in the UK. The general recommendation is 24 in the front and 32 rear. I tried this and found the steering became even heavier. I usually run with 30 all round like you. I think this is fine for general road use. I find that the car understeers terribly during autotests and I often wonder about reducing the front tyre pressure, but then when I look at photos of the car during a test it already looks as though the front tyres are about to peel off the wheel. In fact on the last rally I was one someone was sure they had seen sparks coming from my wheel rim!!
I just had a look in the TR3 hand book and would you believe the recommended pressure for 165 x 15 Michelin and Goodyear tyrs is 24 front and 32 rear at all speeds! For crossplies they recommend 20 front 24 rear, and I always thought that radials ran at lower pressures.
I've leaned something for today - now I can go to bed!

 

[MadMarx]

As the TR's are a little heavier in front the way to go to avoid understeer is more pressure in front and less in rear.

With street tires I had 33 at front and 30 at rear.
Did work fine on trackdays too.

 

[Geo Hahn]

...I find that the car understeers terribly during autotests and I often wonder about reducing the front tyre pressure...

It may be counter-intuitive, but increasing pressure also increases the bite the tire gets so, as noted above, to reduce understeer one would increase the pressure in the front tires.